Diphosphonate-derivatized macromolecules

ABSTRACT

Diphosphonate-derivatized macromolecules, such as proteins, suitable for use as technetium-99m-based scanning agents and as anticalcification agents are disclosed. The scanning agents are prepared by combining Tc-99m in a +3, +4 and/or +5 oxidation state with the diphosphonate-derivatized macromolecules. Also disclosed are pharmaceutical compositions containing these diphosphonate-derivatized macromolecules and methods for scintigraphic imaging using these diphosphonate-derivatized macromolecules labeled with Tc-99m.

TECHNICAL FIELD

This invention relates to diphosphonate-derivatized macromolecules.Specifically, it relates to diphosphonate-derivatized macromoleculeswhich may be radiolabeled with technetium-99 m.

BACKGROUND OF THE INVENTION

The detection and medical/diagnostic assessment of soft-tissue tumorscurrently requires a battery of relatively sophisticated diagnostictests. Generally a physician will utilize every appropriate diagnostictest available when cancer is suspected. These tests utilize imagingequipment for a visual, internal examination and laboratory tests onpotential tumor cells and secretions to determine the tumor burden. If atumor is detected and appears to be malignant, a biopsy is performed toarrive at a diagnosis. Only the biopsy is taken as unequivocal evidenceof malignancy.

The tests involving imaging equipment can be divided into two basictypes: those involving an external energy source, such as X-rays orsound waves, and those involving an internal energy source, such asradioisotopes.

X-ray studies are the most useful tools in staging breast cancer. Themethod is also responsible for detecting the vast majority of lungcancer cases. Once a suspected site has been identified, preciseradiographs can offer valuable information to the physician on the exactlocation and extent of tumors of the breast or lung. Unfortunately, bythe time the tumor is large enough to be detected by X-rays (1-2 cubiccentimeters), the patient's prognosis may be relatively poor. Inaddition to the relatively low sensitivity of X-rays for soft-tissuetumors, serious concerns continue to be raised about the risksassociated with this method's level of radiation exposure.

For breast cancer, the approximate location and size of the tumor can beobtained by ultrasound techniques. Ultrasound provides an image of thetumor from the pattern of echoes arising from high frequency sound wavesimpinging on the breast. Since ultrasonic examination of large sectionsof the body would be difficult to interpret and therefore of littlevalue, this procedure is usually employed for breast examinations aftera palpatable lump has been detected.

Gallium (Ga-67) citrate is the only radiodiagnostic agent indicated fordetermining the presence and extent of certain soft-tissue tumors.Gallium has been shown to be of diagnostic utility in tumors of the lungand liver. In this procedure gallium is dosed intravenously; the galliumis then scanned by a gamma camera seeking an enhanced uptake of galliumin tumor tissue.

Gallium scanning suffers from several important drawbacks. The agent isneither tumor nor disease specific. Gallium will not only concentrate inmany types of tumors (both benign and malignant) to some extent, but italso will seek out any localized infection. Because of thesecharacteristics, the interpretation of scans obtained with galliumcitrate is extremely difficult. The scans usually exhibit low contrastand diffuse areas of radioisotope concentration.

It has been discovered that proteins labeled with a radioisotope areuseful as radiotracers or radioscanners in humans. Examples includeradiolabeled exogenous or autologous plasma protein for diagnostics of,e.g., pulmonary embolism; human serum albumin for blood pool imaging;radiolabeled tumor-specific antibodies for soft tumor imaging;radiolabeled enzyme proteins and hormone proteins for diagnosingmetabolic and endocrinological disorders. The most widely usedradionuclides are iodine-123, iodine-125, iodine-131, indium-111,gallium-67 and technetium-99 m. The iodine isotopes, being a halogen,can irreversibly be incorporated in protein molecules by relativelysimple substitution chemistry. The iodine isotopes are less attractivefor other reasons, especially the beta radiation emitted by theseisotopes and the long half life (8 days) of iodine-131.

Technetium-99 m is generally recognized to be the most desirableradioisotope for radioscanning and radiotracing. Attempts to labelproteins with technetium involve either chelating of the technetium ionby chelating groups inherently present in the protein molecule orderivatizing the protein molecules with a chelating group prior tolabeling with the technetium. A chelate formed by technetium withchelating groups inherently present in the protein is by its nature notstable enough to prevent exchange of technetium with other proteinligands. Technetium-labeled proteins of this type, therefore, often lackthe required biospecificity.

Chelator-derivatized proteins generally involve amino acetic acidcompounds as chelators (e.g. ethylenediaminetetraacetic acid (EDTA) orDTPA). Proteins of this kind have been found to form strong chelateswith indium-111.

Polyphosphonates, in particular diphosphonates, are generally recognizedto be highly desirable ligands for chelating technetium. Prior to thisinvention proteins derivatized with diphosphonates have not beenavailable. It is therefore an object of this invention to providediphosphonate-derivatized proteins suitable for chelating technetium-99m.

It is a further object of this invention to provide a method of labelingthe diphosphonate-derivatized proteins utilizing technetium-99 m withoutdenaturization or loss of biological activity of the protein.

It is still a further object of this invention to provide aprotein-diphosphonate-technetium chelate, and to provide a method forscintigraphic imaging such as soft tumor imaging, in humans utilizingsuch chelates.

BACKGROUND ART

The use of radiolabeled proteins for soft tumor imaging is well known.Early attempts generally involved derivatization of proteins withiodine-123, iodine-125 or iodine-131. It is well-recognized, however,that of the conveniently available radionuclides, technetium has by farthe best nuclear properties for diagnostic imaging (Eckelman et al.,Int. J. Appl. Radiation and Isotopes, 28 (1977), pp. 67-82; Eckelman etal., Cancer Research 40 (1980), pp. 3036-3042).

Attempts have been made to label proteins with technetium. Severalpatents deal with "ligand exchange" and "direct labeling" techniques(U.S. Pat. No. 4,305,922, issued to Rhodes, Dec. 15, 1981; U.S. Pat. No.4,311,688, issued to Burchiel et al., Jan. 19, 1982; U.S. Pat. No.4,323,546, issued to Crockford et al., Apr. 6, 1982). Both methods arebased on the inherent chelating properties of proteins. These complexescan be expected to be unstable in the presence of other proteins, andare therefore not suitable for soft tumor imaging.

Another approach has been the derivatization of proteins usingbifunctional analogs of EDTA (Leung et al., Int. J. Appl. Radiation andIsotopes, 29 (1978), pp. 687-692; Sundberg et al., J. Med. Chem, 17(1974), pp. 1364-1367). The chelating agents are linked to the proteinby a diazo phenyl group. The compounds have been shown to chelateindium-111. This may be due to the fact that EDTA and similar chelatorsprobably do not form very strong complexes with technetium (Deutsch etal., J. Nucl. Med., 21 (1980), pp. 859-866).

U.S. Pat. No. 4,287,362, issued Sep. 1, 1981 to Yokoyama et al.,discloses a bifunctional chelating agent specifically developed forlabeling proteins with technetium. An albumin labeling efficiency ofnearly 100% is reported and the compound provides "a much higher bloodlevel for a longer period of time than conventional technetium-99 mlabeled human serum albumin".

SUMMARY OF THE INVENTION

This invention comprises a diphosphonate-derivatized macromolecules ofthe formula ##STR1## wherein

P is a macromolecule, selected from the group consisting of proteins,polypeptides, polysaccharides, poly(acrylate), poly(acrylamide),poly(methacrylate), poly(ethacrylate), poly(hydroxyalkylmethacrylate),poly(vinyl alcohol), poly(maleic anhydride), poly(maleate) poly(amide),poly(ethylene amine), poly(ethylene glycol), poly(propylene glycol),poly(vinyl acetate) and poly(vinyl benzyl chloride), and furthercontains one or more reactive end groups selected from the groupconsisting of --NH₂, --COOH, --SH, CHO, --S--S, --OH, phenol, guanidino,imidazole or indole and mixtures thereof,

L is a linking moiety selected from the group consisting of ##STR2##

Q is a spacing group selected from the group consisting of substitutedaryl, unsubstituted aryl or C₁ to C₁₂ alkyl, where n is 0 or 1; X isselected from the group consisting of H, OH, NH₂, substituted orunsubstituted amino, halogen or C₁ -C₄ alkyl; and thepharmaceutically-acceptable salts of these derivatized macromolecules.These derivatized macromolecules are suitable for use asanticalcification agents which inhibits biological mineralization ofbioprosthetic devices and soft contact lenses, and also as radiographicimaging agents useful for tumor imaging, radioassays, immunoassays,receptor binding assays or any other scintigraphic procedure whereradiolabeled macromolecules would be used. The derivatizedmacromolecules are suitable for chelating heavy metal ions, inparticular, technetium-99 m. Examples of derivatized proteins arederivatized blood proteins, derivatized enzymes, derivatizedproteinaceous hormones, derivatized antibodies and antibody fragments,connective tissue and cytoskeletal proteins such as collagen, andmyosin.

In its narrower aspect, this invention is directed to derivatizedtumor-specific antibodies or antibody fragments chelated totechnetium-99 m. This invention further provides a method of labelingthe derivatized protein with technetium by in situ reduction of apertechnetate solution without destroying the diphosphonate-protein bondor denaturing the protein leading to significant loss of biologicalactivity. Technetium-protein chelates according to this invention arestable in the presence of plasma proteins; antibody technetium chelatesretain their ability to bind their antigens; and the derivatized proteindoes not have an excessive affinity to bone tissue.

This invention further provides a method for scintigraphic imaging usingdiphosphonate-derivatized molecules chelated with technetium-99 m.

DETAILED DESCRIPTION OF THE INVENTION

This invention comprises a diphosphonate-derivatized macromolecule ofthe general formula: ##STR3## wherein

P is a macromolecule selected from the group consisting of proteins,polypeptides, polysaccharides, poly(acrylate), poly(acrylamide),poly(methacrylate), poly(ethacrylate), poly(hydroxyalkylmethacrylate),poly(vinyl alcohol), poly(maleic anhydride), poly(maleate), poly(amide),poly(ethylene amine), poly(ethylene glycol), poly(propylene glycol),poly(vinyl acetate) and poly(vinyl benzyl chloride) preferably proteins,and further contains one or more reactive end groups selected from thegroup consisting of --NH₂, --COOH, --SH, CHO, --S--S, --OH, phenol,guanidino, imidazole or indole, and mixtures thereof;

L is a linking moiety selected from the group consisting of ##STR4##preferably --N═N--, ##STR5##

Q is a spacing group selected from the group consisting of substituedaryl, unsubstituted aryl or C₁ to C₁₂ alkyl, preferably an unsubstitutedaryl, where n is 0 or 1; and X is selected from the group consisting ofH, OH, NH₂, substituted or unsubstituted amino, halogen or C₁ -C₄ alkyl,preferably H, OH, or NH₂ ; and the pharmaceutically-acceptable salts ofthese derivatized macromolecules.

By "pharmaceutically-acceptable salts" as used herein is meant salts ofthe diphosphonate-derivatized compounds which have the same generalpharmacological properties as the acid form from which they are derived,and which are acceptable from a toxicity viewpoint.Pharmaceutically-acceptable salts include alkali metal (sodium andpotassium), alkaline earth metal (calcium and magnesium), non-toxicheavy metal (stannous and indium), and ammonium and low molecular weightsubstituted ammonium (mono-,di-and triethanolamine) salts. Preferredcompounds are the sodium, potassium, and ammonium salts.

The geminal diphosphonate moieties of the present invention are linkedto the macromolecule via the reactive groups which are part of themacromolecule. The reactive groups on macromolecules needed to link thediphosphonate to the macromolecule are carboxyl (COOH), thiol (SH),amino(NH₂) phenol, aldehyde (CHO), alcohol (CH₂ OH), guanidino,imidazole, indole and disulfide (--S--S) groups. The number ofdiphosphonates which link to the macromolecule depends upon the numberof these reactive groups on the macromolecule. For scintigraphic imagingit is preferable to link at least one diphosphonate per macromolecule,and it is more preferable to link as many diphosphonates on themacromolecule as there are reactive groups, without causing significantloss of biological activity. For inhibition of biologicalmineralization, depending upon properties of the macromolecule, theoptimal degree of derivatization will range from 1% to 90%. Thosemacromolecules which must retain their intrinsic biological activitywill have a lower degree of derivatization (1% to 50%) due to the needto retain their optimal functional biological activity.

Suitable derivatizable macromolecules for use in this invention includeproteins, such as antibodies, antibody fragments, human serum albumin,enzymes, proteinaceous hormones; water-soluble and water-insolublepolysaccharides, such as cellulose, starch, dextran and agar; acrylichomo- and copolymers, such a poly(arylate), poly(acrylamide),poly(methacrylate), poly(ethacrylate), poly(hydroxyalkylmethacrylate),poly(vinyl alcohol), poly(maleic anhydride) and poly(maleate);poly(amides); poly(ethylene imine); poly(ethylene glycol) andpoly(propylene glycol); poly(vinyl acetate); and poly(vinyl benzylchloride).

Other macromolecules suitable for use in the present invention aredisclosed in Jakoby and Wichek (eds.), Methods in Enzymology, Vol. 34,pp. 53-76 (1974) and Mosbach (ed.) Methods in Enzymology, Vol. 44 pp.11-148 (1976), both of which are incorporated by reference.

For scintigraphic imagings virtually any protein is suitable for use inthis invention. However, certain proteins are particularly well-suitedfor specific utilities. For example, radiolabeled proteins for diagnosisof, e.g., pulmonary embolism; human serum albumin for blood poolimaging; radiolabeled enzyme protein and hormone proteins for diagnosingmetabolic and endocrinological disorders; and radiolabeled antibodies orantibody fragments for soft tumor imaging.

The labeled antibodies and antibody fragments useful in the presentinvention are specific to a variety of tumor-associated antigens ormarkers. These markers are substances which accumulate in, on, or aroundtumor cells. They may be intracellular, cell surface or cytoplasmicmarkers. Tumor-specific markers and methods of raising antibodies tothese markers are well known in the art. Such tumor specific markers aredisclosed in Herberman, "Immunodiagnosis of Cancer", in Fleisher (ed.)"The Clinical Biochemistry of Cancer," p. 347 (Am. Assn. Clin. Chem.1979) and in U.S. Pat. No. 4,331,647 to Goldenberg, issued May 25, 1982,and U.S. Pat. No. 4,361,544 to Goldenberg issued Nov. 30, 1982, all ofwhich are incorporated by reference. Methods of raising antibodies invitro are disclosed in Nezlin, "Biochemistry of Antibodies" pp. 255-286(1970), incorporated by reference.

The diphosphonate moieties utilized in the present invention, absent alinking moeity (L), cannot form covalent bonds with the above-mentionedmacromolecules since diphosphonates have no chemical affinity towardsthe protein. L is an atom, group of atoms or a chemical bond whichattaches the geminal diphosphonate moiety separated via a spacer group,if appropriate, to the macromolecule. L is composed of achemically-reactive moiety which can couple to a macromolecule byreaction with the specific reactive end group in the macromolecule.

The linking moiety, therefore, is the result of a reactive species onthe diphosphonate forming a covalent bond with macromolecules. Thedetermination of the appropriate linking moiety is dependent upon theavailability of reactive groups on the macromolecule, i.e., carboxyl,sulfhydryl, disulfide, hydroxy, guandino, imidazole, indole, sulfhydryl,amino, phenol, aldehyde or alcohol groups. Another consideration, in thecase of proteins, is whether or not modification of one or more of thesereactive groups has a significant effect upon the biological activity ofthe protein. Significant loss occurs when the derivatized antibody willno longer localize sufficiently well on the target tissue.

Also within the scope of this invention is a procedure whereby themacromolecule is first pre-activated toward reacting with thediphosphonate. This is accomplished by derivatizing the macromoleculewith a reagent bearing a substituent that would further react with thediphosphonate described in this invention.

The optimum linking moiety to be utilized, therefore, depends upon thereactive end group on the macromolecule to which the diphosphonatemoiety is to be attached.

For example, utilizing proteins for illustration, when the reactivegroup is phenolic group on tyrosine ##STR6## then an appropriate linkingmoiety is a diazo group (--N═N--). This linkage can readily be formed asfollows: ##STR7##

When the reactive end group contains a primary amine, such as the aminoterminus or the epsilon amino group of lysine, an appropriate linkinggroup would be, for example, an amide ##STR8## This linkage can readilybe formed as follows: ##STR9## Other appropriate linking moieties wherethe reactive side chain contains a primary amine include a thiourea##STR10## generated from a phenylisothiocyanate diphosphonate, ##STR11##which reacts with a protein to form: ##STR12## a sulfonamide linkage##STR13## occurs by the reaction of an aryl sulfonyl halide containingdiphosphonate, ##STR14## which reacts with the protein to form:##STR15## an N-carboxyanhydride-containing geminal diphosphonate,##STR16## reacts with an amine containing protein to form an amidelinkage ##STR17## an imidate-containing geminal diphosphonate, ##STR18##reacts with a protein to form an amidine ##STR19## aquinone-diphosphonate can form a disubstituted hydroquinone link asfollows: ##STR20## Schiff base chemistry via an aldehyde-diphosphonate,##STR21## reacts with a protein to form an imine (--N═CH--) link.Reduction of the imine linkage yields: ##STR22## which contains analkylamine linkage.

When the reactive side chain of the protein contains a carboxylic acid,as in aspartic or glutamic acid residues or "C" terminus, theappropriate diphosphonate contains an amino group which reacts with theprotein to form an amide. This linkage can be formed by preactivatingthe protein carboxy group with a water-soluble carbodiimide, thencoupling the reactive intermediate with anomega-aminoalkyldiphosphonate, such as: ##STR23## forming an amide##STR24## linkage when reacted with a protein: ##STR25##

When the reactive group on the protein is a thiol (SH), as in cystene,then an appropriate diphosphonate contains an alkyl halide, for example,##STR26## wherein X=Br or I.

This diphosphonate reacts with the thiol on the protein to form athioether linkage (--CH₂ --S--CH₂ --): ##STR27## iodoacetyldiphosphonates such as ##STR28## reacts with the thiol group on theprotein to form a thioether linkage (--CH₂ --S--CH₂ --): ##STR29##maleimide diphosphonates, such as ##STR30## react withsulfhydryl-containing proteins to form a thioether linkage: ##STR31##

A disulfide linking group can be formed by reacting a 2-pyridinedisulfide agarose gel with a sulfhydryl-containing diphosphonate to forma disulfide link (--S--S--) as follows: ##STR32##

A carbamate linking group can be formed by a polysaccharide, such asreacting Sepherose® or Ficol® (Pharmacia Corporation), with cyanogenbromide to form a reactive imidocarbonate intermediate. A terminalamino-containing diphosphonate will react with the imidocarbonateintermediate to form a substituted carbamate product as follows:##STR33##

The spacer, Q, if needed, creates a space between the protein and thediphosphonate to permit the diphosphonate to be more accessible forradiolabeling. Suitable spacing groups are disclosed in Methods ofEnzymology, Vol. 34 pp. 26-27, incorporated herein by reference. Thespacer can be aryl or C₁ to C₁₂ alkyl. The aryl can be substituted orunsubstitued with one or more substituents. Preferred is anunsubstituted aryl.

The diphosphonate moieties utilized in the present invention(hereinafter diphosphonates) have the formula: ##STR34## where X is H,OH, NH₂, substituted amino, halogen or C₁ -C₄ alkyl, preferred is H, OHor substituted or unsubstituted amino.

These diphosphonates are useful as anticalcification agents forbioprosthetic devices and soft contact lenses. Bioprosthetic devices areknown to undergo biological mineralization, generally this mineralcomponent is composed of calcium phosphate. When this calcium builds up,the function of the device is impaired. The diphosphonate-derivatizedmacromolecules of the present invention when linked to such devicesinhibit mineralization.

Diphosphonates can be attached to proteins, such as collagen, in heartvalve and vascular graft implants. For example a water solublecarbodiimide is added to collagen for activation, this activatedintermediate, ##STR35## is then reacted with collagen to form: ##STR36##a diphosphonate-derivatized insoluble protein which will resistbiological mineralization.

Covalent attachment of diphosphonates to extended wear soft contactlenses inhibit their calcification. These soft lenses are often composedof poly(acrylamides), polyols or polycarboxylates. The lens polymer canbe reacted with a water soluble carbodimide, for example:

    polymer --COOH+R--N═C═N--R'

to form a reactive intermediate: ##STR37##

This intermediate can then be reacted with a diphosphonate to form adiphosphonate-derivatized polymer: ##STR38##

SCINTIGRAPHIC IMAGING AGENT

The diphosphonate-dervatized macromolecules are useful as scintigraphicimaging agents when chelated with technetium-99 m. Methods of labelingthe phosphonate moiety with Tc-99 m are disclosed in Castronovo et al.,"The Phosphonate Moiety: Labeling with 99 m-Tc(Sn) After SyntheticAttachement to Diverse Biological Compounds", Radiopharm. [InternationalSymposium], Chapter 7, pp. 63-70 (1975), incorporated herein byreference.

Generally, the diphosphonate-derivatized macromolecule is treated with asolution containing stannous ion. To this mixture is added a solution ofTc-99 m as pertechnetate. The Tc-99 m is reduced by the stannous ionforming a coordinate covalent linkage with the diphosphonate.

As used herein the term "pertechnetate reducing agent" includescompounds, complexes or the like, comprising a reducing ion capable ofreducing heptavalent technetium (TcO₄ ⁻) to trivalent, tetravalentand/or pentavalent technetium. Free metals, such as tin, are also knownfor use as pertechnetate reducing agents, although undissolved metalmust be removed from the scanning solution prior to injection into thepatient. Suitable pertechnetate reducing agents include sodiumhydrosulfite, as well as metalic salts of sulfuric acid and hydrochloricacid, such as stannous chloride.

The compositions herein optionally, and preferably, contain astabilizing amount of a stabilizer material to prevent or inhibit theoxidation of the pertechnetate reducing agent (e.g., oxidation of Sn⁺²to Sn⁺⁴) during storage and/or to inhibit or diminish the reoxidation ofreduced technetium-99 m and/or to diminish the formation oftechnetium-labeled impurities which may form during use of thecompositions.

The stabilizers used herein are characterized by their toxicologicalacceptability under the conditions of use, their ability to stabilizethe product for a reasonable period of storage and/or under usageconditions, and by their substantial non-interference with the deliveryof the technetium radionuclide to, for example, soft tumors.

Stabilizers which meet the foregoing requirements and which are suitablefor intravenous injection include gentisic acid and its water-solublesalts and esters, ascorbic acid and its water-soluble salts and esters,and erythorbic acid and its water-soluble salts and esters. Gentisicacid, ascorbic acid and erythorbic acid are all known,commercially-available materials. The sodium salts of these acids arealso all commercially-available, quite water-soluble, and preferred foruse herein.

As is known in the literature, stabilizer materials such as ascorbicacid can chelate or complex with technetium and cause it to be depositedin uncalcified soft tissue. Since the practitioner of the presentinvention will wish to avoid all unnecessary deposition in soft tissue,it will be appreciated that the amount of stabilizer materialsoptionally used in the present compositions should not be so great as toovershadow the tumor directing effect of the derivatized macromolecule,thereby interfering with the imaging.

The scintigraphic imaging agents of the present invention are intendedfor systemic or oral administration into humans or lower animals.Accordingly, appropriate manufacturing and operating conditions areemployed to provide suitably sterile compositions.

For gastrointestinal imaging, oral administration would be theappropriate method of administration. For soft tissue tumor imaging, theappropriate route of administration would be intravascular orintralymphatic. For blood pool imaging, intravenous administration wouldbe the appropriate method.

The compositions of the present invention can be prepared by simply drymixing the technetium reducing agent and the derivatized macromolecule.The optional stabilizer can also be dry blended into such mixtures, ascan additional, non-interferring agents, such as sodium chloride.

In an alternate mode, the compositions herein can be provided inlyophilized form. Such compositions are prepared by co-dissolving thediphosphonate-derivatized macromolecule and the technetium reducingagent in an aqueous solution, together with any desired optionalstabilizers, and lypholizing the composition using standard equipment.Preferably, sterile, deoxygenated water is used in processing and theproduct is stored under nitrogen. Although somewhat more complicated tomanufacture than the dry mixed product, the lypholized product offersthe advantage that water-insoluble particulate matter which might bepresent in the raw materials can be removed by filtration prior to thefreeze drying step.

In another mode, the compositions herein can be provided as aqueoussolutions in pharmaceutically-acceptable liquid carriers. These carrierscan be, for example, saline solution or sterile, pyrogen-free water.Preferably, the water is deoxygenated and the composition is storedunder nitrogen, thereby minimizing undesirable oxidation of thepertechnetate reducing agent on storage. Since the reducing agent ismore prone to oxidize in solution than in the dry powder andfreeze-dried composition forms, it is preferred that aqueouscompositions contain a stabilizer.

The compositions of the present invention are prepared such that theweight ratio of the derivatized macromolecule: technetium reducing agentis from about 2:1 to about 100,000:1, preferably from about 2:1 to about10,000:1.

Stabilized compositions are generally formulated such that the weightratio of derivatized macromolecule: stabilizer is from about 1:1 toabout 10,000:1, preferably from about 1:1 to about 1,000:1.

Preferred stabilized compositions in unit dosage form contain from about0.05 mg. to about 3 mg. of the stannous reducing agent; from about 0.25mg. to about 1.0 mg. of the gentisate or ascorbate stabilizer; and fromabout 0.01 to about 50 mg. of the diphosphonate-derivatizedmacromolecule.

Compositions of the foregoing type are characterized by aphysiologically-acceptable in-use solution pH in the range from about3.5 to about 8.5, and, preferably, fall within a pH range of about 4.5to about 7.4.

In the case of proteins, a liquid pharmaceutical composition suitablefor scintigraphic imaging would be composed of from about 0.01% to about20% of the diphosphonate-derivatized protein with the remainder beingpertechnetate reducing agent, stabilizer, and apharmaceutically-acceptable carrier. In the case of othermacromolecules, from about 1% to about 20% of the total compositionwould be comprised of the diphosphonate-dervatized macromolecule.

In the case of proteins, a lyophilized pharmaceutical composition wouldbe composed of from about 1% to about 50% of thediphosphonate-derivatized protein. For other macromolecules, from about5% to about 99% of the composition would be comprised of thediphosphonate-derivatized macromolecule.

In use, the compositions are mixed with a pertechnetate-99 m isotonicsolution from a commercial technetium source to yield a Tc-99 m labeleddiphosphonate-derivatized macromolecule suitable for systemic or oraladministration. The stability of such scanning agents is ample underordinary hospital conditions. Administration is preferably done withinabout eight hours after addition of the pertechnetate solution. Forintravenous administration, the concentration of reagents and technetiumradionuclide is sufficient such that about 1 ml. of the solution isadministered to an adult of about 50-100 kg. body weight. One ml. ofsolution is preferably injected intravenously over a period of about 30seconds. For oral administration, the concentration of reagents andtechnetium radionuclide is sufficient such that from about 10 ml toabout 150 ml of the solution or suspension is administered to an adultof about 50-100 kg body weight. Follow up scans would consist of thesame levels of administration.

The actual structure of the reaction product formed by the 99 mTc/diphosphonate-derivatized macromolecule reducing agent mixture andintroduced into the body is not known with certainty.

These diphosphonate-derivatized macromolecules are useful for anybio-analytical technique where radiolabeled proteins would be used. Suchapplications include tumor imaging, radioimmunoassays, myrocardiolinfarction assays, thrombosis imaging, receptor binding assays and bloodpool imaging, and gastrointestinal imaging.

Generally, a safe and effective amount of the radiolabeled macromoleculeis administerd systemically or orally for the scintigraphic imagingprocedures of the present invention.

By "safe and effective amount" as used herein is meant an amount of thecomposition high enough to provide a clinically useful scintigraphicimage, but low enough to avoid serious side effects (at a reasonablebenefit/risk ratio), within the scope of sound medical judgment. Thesafe and effective amount of the composition will vary with theparticular scintigraph technique and particular clinical condition beingevaluated, the age and physical condition of the patient being treated,the severity of the condition, the duration of treatment, the nature ofconcurrent therapy and the specific diphosphonate-derivatizedmacromolecule employed.

Systemic administration would be appropriate for tumor imaging,myrocardial infarction assays, thrombosis imaging, receptor bindingassays, and blood pool imaging.

The following nonlimiting examples illustrate the compounds, chelates,compositions, methods and uses of the present invention.

EXAMPLE I

This example demonstrates, protein derivatization of sodium [2-(4aminophenyl)-ethane 1,1-diphosphonate].

Sodium [2-(4-aminophenyl)ethane-1,1-diphosphonate] was synthesized bythe following method: ##STR39## Specifically, to a slurry of 10.0 g(0.25 mole) of potassium hydride in 200 ml dry toluene, cooled to 5° C.,was added dropwise 72.5 g (0.25 mole) of tetraethylmethanediphosphonate. This reaction was carried out under a nitrogenatmosphere allowing the hydrogen gas generated to be swept away. Thediphosphonate anion solution was brought to room temperature after allthe ester had been added. 54 grams (0.25 mole) of p-nitrobenzylbromidewas dissolved in 200 ml warm, dry toluene. The toluene solution of thehalide was added rapidly to the diphosphonate anion solution. Thereaction was somewhat exothermic causing a temperature rise to 85° C.The mixture was stirred at room temperature for 2 hours. The KBr thatformed was filtered off and the toluene evaporated on a rotaryevaporator. Then 250 ml of water was added to the remaining oil and themixture extracted 2 times with 250 ml diethyl ether. The ether phase wasdried with anhydrous magnesium sulfate, filtered and evaporated. Theresulting oil was dissolved in 250 ml of ether and the solution wasextracted 2 times with 100 ml water to remove the unreactedtetraethylmethane diphosphonate which is quite water soluble. The etherlayer was dried with magnesium sulfate and evaporated yielding 76 gramsof the crude ester: tetraethyl2-(p-nitrophenyl)-ethane-1,1-diphosphonate.

Twenty-two grams of this crude ester was added to 250 ml ethanol in a500 ml Parr hydrogenation bottle. A 10% Pd/charcoal catalyst (1.5 g) wasadded and the mixture was shaken under a 50 psig hydrogen atmosphererepressurizing as necessary. After 4.5 hours, the reaction was complete.The solid was filtered off and the ethanol evaporated. Two hundred fiftyml of 6N HCl was added to this crude product that contained a mixture ofmono- and dialkylated methanediphosphonate. The mixture was refluxedovernight. The reaction mixture was cooled and evaporated to dryness ona rotary evaporator. Two hundred ml distilled water was added to theresidue. The mixture was warmed to approximately 60° C. for 1 hour andthen cooled to room temperature. A substantial amount of insolubleprecipitate remained. This is the desired product. It was filtered offand slurried in 150 ml of water. The pH was adjusted to 4.2 with 50%sodium hydroxyide solution. The solution was heated to boiling andfiltered hot. Two hundred ml of ethanol was added slowly to the warmsolution causing a precipitate to develop. This solution was cooled in arefrigerator overnight. The precipitate, the sodium salt of the desiredproduct, was filtered off, washed with methanol and air dried. Theresult was 6.2 grams of sodium[2-(4-aminophenyl)-ethane-1,1-diphosphonate].

The sodium [2-(4-aminophenyl)-ethane-1,1-diphosphonate] (0.3 mg, 0.1mmol) was dissolved in 0.5 ml of H₂ O, chilled in an ice-bath, and thenacidified with 0.5 ml of concentrated HCl. To this clear solution wasadded dropwise 0.25 ml of chilled 0.5M (0.125 mmole) NaNO₂ solution. Thepale yellow solution was stirred for 1.5 hour at 0° C., then treatedwith 3 mg of urea to destroy excess nitrate. The reaction mixture wasthen diluted to 10 ml. The desired amount of diazonium salt reagent wasremoved from this stock solution, neutralized with solid NaHCO₃, andadded dropwise to a 0° C. solution of rabbit IgG (obtained from SigmaChemical Corporation) (60 mg) in 3 ml of 0.05M pH8 phosphate buffer. Thereaction mixture was stirred overnight at 4° C., then dialyzedexhaustively against 0.1M NaC1 solution at 4° C. The solution ofderivatized protein was stored in the refrigerator.

The resultant solution of derivatized protein was analyzed according tothe standard Biyret analysis for determining protein concentration asdisclosed in Bulletin #690, Sigma Chemical Co., St. Louis, Mo.

The degree of derivatization, in terms of average number of azo groupsin the derivatized protein solution, was calculated from the solution'sabsorbance at 350 nm (E=20,000). The protein concentration wasdetermined from its characteristic absorbance at 280 nm. It wasnecessary to make a slight correction for the protein concentration dueto small degree of absorbance of the azo phenyl group at 280 nm(E=19,800). The ratio of azo concentration to the corrected proteinconcentration then gives the average number of azo linkages per proteinmolecule.

The number of azo groups per protein molecule was calculated as follows:

For the derivatization of rabbit IgG using a molar ratio of 25:1diazonium salt to protein, the following procedure was used to determinethe average number of diphosphonate groups bound to each proteinmolecule.

    Measured absorbances: A.sub.350 =0.262, A.sub.280 =1.546

Calculation of azo concentration: (E_(m) for azo=22,000)

at 350 nm:

    A=0.262=22,000×C.sub.azo

    C.sub.azo =1.19×10.sup.-5 M

Calculation of azo phenyl absorbance at 280 nm: (E_(m) for azophenyl=19,800)

    A=19,800×1.19×10.sup.-5 M=0.236

Calculation of protein concentration (A₂₈₀ for rabbit IgG=219,000):

    A=1.546-0.236=1.31=219,000×C.sub.protein

    C.sub.protein =5.98×10.sup.-6 M

Calculation of azo group per protein molecule ##EQU1##

EXAMPLE II

The following example illustrates the binding of technetium-99 m todiphosphonate-dervatized IgG and F(ab')₂ fragments.

Rabbit IgG (obtained from Sigma Corporation) was derivatized and labeledwith 99 m-Tc as described in Example III except without gentisic acid.Between 2 and 3 mg of IgG or derivatized IgG were labeled with 500 μCi99 m-TC. The reaction mixture was gel filtered over a column of BioGelP6 (Bio Rad) and 1.0 mg of the peak protein fractions were taken for thefollowing plasma exchange experiments.

An aliquot of 99 m-Tc labeled DP derivatized IgG was added to 1.0 ml offreshly prepared heparinized human plasma. Underivatized, 99 m-Tclabeled IgG was treated identically and used as a control. The combinedIgG-plasma was heated at 37° with continuous agitation. After 30minutes, an excess of goat anti-rabbit γ-globulin (GARGG) was added toprecipitate the rabbit IgG. Following centrifugation, the rabbit IgGprecipitate and the plasma supernatant were subjected to γ-counting. Any99 m-Tc which remained associated with the rabbit IgG was found in theprecipitate. The results are summarized in the following Table:

    ______________________________________                                                    99m-Tc bound                                                                              % 99mTc which does                                    mole DP per per mg IgG  not exchange with                                     mole IgG    (counts/100 sec)                                                                          plasma components                                     ______________________________________                                        0           1.13 × 10.sup.5                                                                     37%                                                   0.3         3.47 × 10.sup.5                                                                     84%                                                   1.9         3.82 × 10.sup.5                                                                     87%                                                   8.0         4.81 × 10.sup.5                                                                     91%                                                   ______________________________________                                    

The diphosphonate-derivatization procedure of the present invention doesnot significantly alter the activity of the antibody as estimated bythese competitive binding studies. The addition of the diphosphonate didincrease the affinity of antibodies for binding with 99 m-Tc.

These data demonstrate that DP-IgG not only binds more 99 m-Tc than doesunderivatized IgG, but the 99 m-Tc is bound more tightly to DP-IgG asjudged by the high percentage of 99 m-Tc which does not dissociate fromDP-IgG. Substantially similar results are obtained when F(ab)₂ fragmentsrather than IgG fragments were characterized.

EXAMPLE III

This example illustrates in vivo imaging of soft tissue tumor usingDP-IgG and DP-F(ab')₂

IgG and F(ab')₂ fragments were prepared from commercially availablerabbit antisera to human β₂ M and human CEA. For CEA, the IgG fractionas prepared by the supplier was used, while rabbit anti β₂ M was furtherpurified using an affinity column of immobilized human β₂ M.

IgG and F(ab')₂ fragments were derivatized as described above in ExampleI. The stoichiometric ratio of the reactants, diphosphonate: protein,was 10:1. After exhaustive dialysis against phosphate buffered saline atpH 7.4, 1.0 mg each of IgG and F(ab')₂ fragment were freeze-dried.

In preparation for labeling with 99 m-Tc and injection, the freeze-driedproteins wre dissolved in 700 μl sterile H₂ O. One hundred twenty-fivemicrograms of gentisic acid, 4 mCi Tc-99 m as TcO₄ ⁻, and 250 μg SnC1₂were then added to each vial. Injections of 220-250 μl were made intothe tail vein of athymic mice bearing either a human colonic carcinomatumor which expresses CEA, or a human prostatic carcinoma tumor whichexpress β₂ M. Scintigraphs were obtained on a Technicare Sigma 400 gammacamera at 1, 4 and 24 hours post-injection using a pinhole columnator.At 24 hours after dosing, animals receiving anti β₂ M IgG and F(ab')₂fragments were sacrificed, tumors excised and half of each tumor wasfixed in 10% neutral buffered formalin. The other half of each tumor wasembedded and frozen for indirect immunofluorescence.

At 4 hours post-injection the anti β₂ M IgG and its F(ab')₂ fragmentsshowed good tumor localization.

Immunohistochemical evaluation of the tumors, excised 24 hours afterinjection of the IgG or F(ab')₂ fragments, demonstrated that the IgG andF(ab')₂ fragments did reach the tumor.

EXAMPLE IV

This example demonstrates the use of a diphosphonate-derivatizedinsoluble macromolecule for use as a gastrointestinal imaging agent.

10 g Sepherose CL-4B (a polysaccharide obtained from PharmaciaCorporation) was added to 10 ml distilled H₂ O. The sample was activatedin 2M Na₂ CO₃ solution using cyanogen bromide dissolved in acetonitrile(2 g. CNBr/ml CH₃ CN). The Sepherose was stirred vigorously at roomtemperature for 2 minutes. The resin was filtered off, washed with 0.1 NNaHCO₃ pH=9.5 and then with H₂ O. The activated gel was added to 30 ml0.2M NaHCO₃ pH 9.7 to which 1.5 g2-(4-aminophenyl)ethane-1,1-diphosphonic acid had been added. Thismixture was reacted overnight in a refrigerator (4° C.). The gel wasfiltered off. 2M glycine was added at pH=9.5 to the gel (to quench theunreacted sites). The derivatized gel was then washed with excess water.The pH of the slurry was adjusted to 5.0 with hydrochloric acid.

To test for Tc-99 m binding to the gel, the following experiment wascarried out:

0.5 g derivatized CL-4B was mixed with 3 ml distilled water and 50 μl ofa stock solution of 120 mg. SNCl₂ .2H₂ O dissolved in 5 ml 0.1 N HCl. Tothis slurry was added 240 Ci Tc-99 m TcO₄ ⁻ solution in saline. The vialwas shaken for 2-3 minutes and then filtered through a 0.45 syringefilter.

The activity in the syringe and filter as well as in the filtrate wasmeasured. 97.5% of the technetium remained associated with the gel. Acontrol experiment using underivatized Sepherose® CL-4B was run asdescribed above and only 21.6% of the technetium remained associatedwith the gel.

EXAMPLE V

This example demonstrates formation of a diphosphonate-derivatizedpolysaccharide gel containing a disulfide linking group.

A (glutathione-2-pyridyl disulfide) agarose conjugate is prepared asdescribed in Methods in Enzymology 34 pp 536-538. This gel (Agarose-GS-2pyridyl) is reacted with an excess of 4-mercaptobutane-1,1-diphosphonatein phosphate buffered soluton at pH=8. After reaction, the gel is washedexhaustively on a glass filter using isotonic saline.

The product formed is: ##STR40##

EXAMPLE VI

This example demonstrates formation of a diphosphonate-derivatizedalbumin containing a thiourea linkage suitable for use in a lung imagingformulation.

The 2-(4-aminophenyl)ethane-1,1-diphosphonate described in Example I isconverted to 2-(4-isothiocyanatophenyl)ethane-1,1-diphosphonate bytreatment with a 10 fold molar excess of thiophosgene in 0.4M NaHCO₃aqueous buffer at room temperature. The reaction solution is extractedwith dichloromethane to remove unreacted thiphosgene. Thisisothiocyanate diphosphonate-containing solution is reacted with asuspension of aggregated albumin particles, 15 mg of albumin (10μ-100μdiameter) in 25 ml 0.4M NaHCO₃ buffer, pH=8.5, for 60 minutes at 37° C.Following reaction the diphosphonate-derivatized albumin aggregates arecollected and washed by centrifugation to remove untreateddiphosphonate.

The product formed is: ##STR41##

EXAMPLE VII

The example demonstrates photo-induced coupling of a diphosphonate to anantibody fragment.

The diazophenylethane-1,1-diphosphonate described in Example I isconverted to 2-(4-azophenyl)-ethane-1,1-diphosphonate by treatment withan aqueous solution of sodium azide at pH=9 and 4° C. The product isrecovered by precipitation from the reaction solution with ethanol. Onemg of F(ab')₂ fragment of anti-β₂ M macroglobulin described in Example Iis mixed with 10 mg of the above azidophenyl diphosphonate dissolved in5 ml of phosphate buffered saline at 4° C. Irradiation is carried outusing a Rayonet Minireactor at 240-350 nm. The nitrene intermediateformed upon photolysis couples to the protein molecules. Followingreaction the excess diphosphonate is removed by gel permeationchromatography on a Sephadex G-25 column.

EXAMPLE VIII

Aminoethyl cellulose previously washed with 0.5M NaOH and water issuspended in 0.05M phosphate buffer pH=7 (10 g dry weight in 250 ml).Twenty ml of a 25% w/v solution of glutaraldehyde is added. After 2 hrof stirring at room temperature, the cellulose derivative is recoveredby filtration and washed with water. The product is resuspended in thesame buffer and treated with 2.0 g of5-aminopentane-1-hydroxy-1,1-diphosphonate. After stirring at roomtemperature for 3 hours, the cellulose is recovered by filtration andwashed exhaustively with water to remove the untreated diphosphonate.

The product formed is: ##STR42##

EXAMPLE IX

The diphosphonate-derivatized aminoethyl cellulose from Example VIII istreated with an aqueous solution of sodium borohydride at pH=9.5. Thischemical reduction process stabilizes the imine linkage formed inExample VIII yielding a more stable dialkylamine linkage.

The product formed is: ##STR43##

EXAMPLE X

A clear hydrogel copolymer film containingpoly(hydroxyalkylmethacrylate) is suspended in borate buffer that is 10%w/v in cyanogen bromide buffer at pH=11. The pH is maintained at pH=11with 4N NaOH solution. After activation with cyanogen bromide, thepolymer film is treated overnight with a 50 mmolar solution of6-amino-1-hydroxyhexane-1,1-diphosphonate at pH=9 in 0.5M NaHCO₃ buffer.The derivatized polymer film is washed exhaustively in distilled waterto remove unreacted diphosphonate.

The product formed is: ##STR44##

What is claimed is:
 1. A radiolabeled diphosphonate-derivatizedpolypeptide chelate comprising technetium 99 m complexed with adiphosphonate-derivatized polypeptide selected from the group consistingof:wherein (i) P is a polypeptide; (ii) n is an integer from 1 to 12;and (iii) X is selected from the group consisting of H, OH, and NH₂,substituted amino, halogen and C₁ -C₄ alkyl;and thepharmaceutically-acceptable salts of these derivatized polypeptides. 2.The radiolabeled chelate of claim 1 wherein saiddiphosphonate-derivatized polypeptide is selected from the groupconsisting of ##STR45##
 3. The radiolabeled chelate of claim 1 whereinsaid diphosponate-derivatized polypeptide is selected from the groupconsisting of: ##STR46##
 4. The radiolabeled chelate of claim 1 whereinX is selected from the group consisting of NH₂, OH and H.
 5. Theradiolabeled chelate of claim 2 wherein X is selected from the groupconsisting of NH₂, OH and H.
 6. The radiolabeled chelate of claim 3wherein X is selected from the group consisting of NH₂, OH and H.
 7. Theradiolabeled chelate of claim 6 wherein X is OH and n is an integer from1 to
 5. 8. A pharmaceutical composition for scintigraphic imaging inhumans or animals which comprises:(a) a safe and effective amount of adiphosphonate-derivatized polypeptide selected from the group consistingof: ##STR47## wherein (i) P is a polypeptide;(ii) n is an integer from 1to 12; and (iii) X is selected from the group consisting of H, OH, andNH₂, substituted amino, halogen and C₁ -C₄ alkyl; and thepharmaceutically-acceptable salts of these derivatized polypeptides; (b)a pertechnetate reducing agent; (c) a stabilizer compound; and (d) apharmaceutically-acceptable carrier.
 9. The composition of claim 8wherein said diphosphonate-derivatized polypeptide is selected from thegroup consisting of: ##STR48##
 10. The composition of claim 9 wherein Xis selected from the group consisting of NH₂, OH and H.
 11. Acomposition of claim 10 wherein X is OH and n is an integer from 1 to 5.12. A pharmaceutical composition according to claim 8 in liquid formcomprising from about 1% to about 20% of the diphosphonate derivatizedpolypeptide, from 0.0001% to about 10% of a pertechnetate reducingagent, from about 0.001% to about 20% of a stabilizer and from about 50%to about 98% of a pharmaceutically-acceptable carrier.
 13. Apharmaceutical composition according to claim 8 in liquid formcomprising from about 0.01% to about 20% of thediphosphonate-derivatized polypeptide, from about 1×10⁻⁶ % to about 10%of a pertechnetate reducing agent, from about 1×10⁻⁵ % to about 20% of astabilizer compound and from about 50% to about 99.9% of apharmaceutically-acceptable carrier.
 14. A pharmaceutical compositionaccording to claim 8 in lyophilized form.
 15. A lyophilizedpharmaceutical composition according to claim 14 comprising from about5% to about 99% of the diphosphonate-derivatized polypeptide, from about0.0005% to about 10% of a pertechnetate reducing agent, from about0.005% to about 20% of a stabilizer and from about 0.01% to about 60% ofa pharmaceutically-acceptable carrier.
 16. A lyophilized pharmaceuticalcomposition according to claim 14 comprising from 1% to about 50% of thediphosphonate-derivatized polypeptide, from about 0.0001% to about 10%of a pertechnetate reducing agent, from about 0.001% to about 20% of astabilizer and from about 20% to about 98% of apharmaceutically-acceptable carrier.
 17. A method for scintigraphicimaging of tissues in humans or animals which comprises mixing thepharmaceutical composition of claim 8 with a pertechnetate-99 msolution, administering from about 1 ml to about 150 ml of said mixtureto said human or animal and subsequently imaging said human or animalwith a scintigraphic device capable of detecting the radiation emittedfrom said mixture.
 18. A method for scintigraphic imaging of tissues inhumans or animals which comprises mixing the pharmaceutical compositionof claim 13 with a pertechnetate-99 m solution, administering from 1 mlto about 150 ml of said mixture to said human or animal and subsequentlyimaging said human or animal with a scintigraphic device capable ofdetecting the radiation emitted from said mixture.